In industry, oily waste waters are produced in various processes located in the steel and aluminum industries, chemical processing industry (CPI), automotive industry, laundry industry and refinery industry. In these industries, highly refined oils, lubricants and greases contact water for various purposes according to the particular industry. This results in a highly dispersed or severe oil-in-water emulsion in the waste water streams.
For example, in the steel and aluminum industries, waste water from steel and aluminum mills using hot rolling mills contain lubricating and hydraulic pressure hydrocarbons. Waste water from cold rolling mills contains oils that lubricates the sheets and reduces rust. Specifically, in cold rolling mills, oil-in-water emulsions are sprayed on the metal during rolling to act as coolants. Also, metalworking plants generate waste water streams containing lubricating and cutting oils, lapping and deburring compounds, grinding and other specialty fluids. These oils are generally highly refined hydrocarbons.
Refinery waste oil comes from two different sources: (1) Skimmings from the water clarification equipment, i.e., DAF's, API separators, and consisting mainly of crude oil; and, (2) Leakage from processes collected via traps and drains throughout the plant. This oil is usually sent to a waste water treatment plant.
One type of waste oil is formed during the process of removing dispersed oil from waste water in waste water treatment plants. The oil (called "float" or "skimmings") is concentrated in clarification vessels such as dissolved air floatation units (DAFs), induced gas floatation units (IGFs), corrugated plate interceptors (CPIs), and holding tanks. The oil floats to the top of these units, is removed by mechanical means and then stored. This waste oil may then be disposed of by incineration, sent to oil reclamation sites, or treated on-site. These waste oils have a minimum of 50% to 95% oil and contain emulsified water and solids which are stabilized by chemicals used to remove the oil from the waste water.
Waste waters from cotton and wool manufacturing plants contain oils and greases from the scouring, desizing and finishing operations. Finishing oils used in cotton and wool manufacturing to reduce friction and snagging of fibers on spinning machines end up in the waste water. Processes in other industries also generate oily waste water such as: paints, surface coatings, and adhesives; soaps and detergents; dyes and inks; and the leather industry. In each of the industries described above, the oils used in process ultimately contaminate waste water streams as highly dispersed or oil-in-water emulsions.
The emulsified oil in the waste water is typically present in the range of several hundred to tens of thousands of ppm. It is critical to remove this oil from an environmental standpoint. The United States Environmental Protection Agency has placed fight restrictions on total oil and grease (TOG) limits for water that is to be discharged into public drinking water supplies or into open bodies of water. The removal of this oil is very critical to the established discharge limits for total dissolved solids (TSS), carbon oxygen demand (COD), biological oxygen demand (BOD) and total organic carbon (TOC) into local sewers and rivers. Not only has the EPA established severe limits on the oil and grease discharge, these industries are affected by local city ordinances as well.
An emulsion is an intimate mixture of two liquid phases, such as oil and water, in which the liquids are mutually insoluble and where either phase may be dispersed in the other. An oily waste emulsion, in which oil is dispersed in the water phase, may contain any of a variety of oils in a wide range of concentrations. These oils are defined as substances that can be extracted from water by hexane, carbon tetrachloride, chloroform, or fluorocarbons: In addition to oils, typical contaminants of these emulsions may be solids, silt, metal particles, emulsifiers, cleaners, soaps, solvents, and other residues. The types of oils found in these emulsions will depend on the industry. They may be lubricants, cutting fluids, heavy hydrocarbons such as tars, grease, crude oils, and diesel oils, and also light hydrocarbons including gasoline, kerosene, and jet fuel. Their concentration in the waste water may vary from only a few pans per million to as much as 5 to 10% by volume.
A stable oil-in-water emulsion is a colloidal system of electrically charged oil droplets surrounded by an ionic environment. Emulsion stability is maintained by a combination of physical and chemical mechanisms.
Emulsions may be broken by chemical, electrolytic, or physical methods. The breaking of an emulsion is also called resolution, since the aim is to separate the original mixture into its parts. Chemicals are commonly used for the treatment of oily waste waters, and are also used to enhance mechanical treatment. In breaking emulsions, the stabilizing factors must be neutralized to allow the emulsified droplets to coalesce. The accumulated electric charges on the emulsified droplet are neutralized by introducing a charge opposite to that of the droplet. Chemical emulsion breakers provide this opposite charge, and are thus usually ionic in nature.
The treatment of oily waste water is normally divided into two steps, i.e., coagulation which is the destruction of the emulsifying properties of the surface active agent or neutralization of the charged oil droplet, and flocculation which is the agglomeration of the neutralized droplets into large, separable globules. The term oily waste water refers to an oil-in-water emulsion which may contain oil, dispersed solids, and water.
Traditionally, sulfuric acid has been used in oily waste treatment plants as the first step in emulsion breaking. Acid converts the carboxyl ion in surfactants to carboxylic acid, allowing the oil droplets to agglomerate. Chemical coagulating agents, such as salts of iron or aluminum, can be used in place of acid, with the additional benefit that these aid in agglomeration of the oil droplets. Some examples of inorganic emulsion breakers useful in oil-in-water emulsions are: polyvalent metal salts such as alum, AlCl.sub.3, FeCl.sub.3, and Fe.sub.2 (SO.sub.4).sub.3, mineral acids such as H.sub.2 SO.sub.4, HCl, and HNO.sub.3, and adsorbents such as pulverized clay and lime. However, the aluminum or iron forms hydroxide sludges that are difficult to dewater. Acids generally break emulsions more effectively than coagulant salts, but the resultant acidic waste water must be neutralized after oil/water separation.
As described above, metal ions, such as, Fe.sup.3+, Zn.sup.2+, Al.sup.3+, etc., have long been used to break oil-in-water emulsions, but recent government regulations have restricted their levels in discharged streams. Although effective at breaking oil-in-water emulsions, they too require another chemical to flocculate the oil.
Organic demulsifiers are extremely effective emulsion breaking agents, giving more consistent results and producing better effluent quality than an inorganic program. In many treatment plants, organic emulsion breakers have replaced traditional alum treatment for exactly those reasons. In addition to yielding a better quality effluent, organic emulsion breakers often require lower dosages than a corresponding inorganic treatment. Organic emulsion breakers reduce the amount of sludge generated in a treatment program by as much as 50 to 75%. Some examples of organic emulsion breakers useful in oily waste waters are polyamines, polyacrylates and their substituted copolymers.
Historically, dry polymers, solution polymers, and inverse emulsion latexes have been used to treat the waste water. Each material has its own advantages and disadvantages. While dry polymers have the benefit of being extremely concentrated, thereby reducing shipping costs, the equipment to dissolve the polymers is expensive and is not available to all end-users on site.
Water-in-oil emulsions of water-soluble vinyl addition polymers, referred to herein as latex polymers are used quite frequently, though they have several disadvantages. The first is that the latex polymer must be inverted prior to use, which complicates the process of feeding the polymer into the system. Numerous problems associated with this feeding method have caused many customers to avoid latex polymers. Additionally, the latexes generally have a very narrow treating range, often resulting in over-treatment at higher dosages. Furthermore, latex polymers add even more oil to the stream to be treated because latex polymer preparations include 30-35% solids dispersed in oil. Of course, adding more oil to the system is undesirable when treating waste water streams.
Although solution polymers require no prior make up, percent solids and molecular weight characteristics of these polymers are severely limited due to the nature of the material. These materials are often used to break oil-in-water emulsions, but they are unable to flocculate the dispersed oil, thus requiring an adjunct chemical to complete the process.
The water-soluble polymers of the invention offer many solutions to these problems and represent a new method for industrial waste water demulsification. While no particular form of the polymer is crucial for activity, for ease of handling the solution form of the copolymer is preferred.
The present inventors have developed various novel hydrophobically modified polyelectrolyte copolymers which may be used as demulsifiers for oily waste waters. These cationically charged hydrophobically modified polymers, which incorporate into the polymer backbone a vinyl alkoxysilane, exhibit improved performance or activity in demulsification than do conventional inorganic and organic treatments. The unique cationic and surface active polymers of this invention are advantageous over conventional polymers because they are capable of both increased surface activity, as evidenced by lowered surface tension, and adsorption onto hydrophobic surfaces.
The advantages of the diallyldimethylammonium chloride/vinyl trialkoxysilane copolymers stem from the fact that they have the following characteristics: 1) silicon components are capable of forming networks with other silicon moieties, similar to crosslinking; and 2) incorporated silicon functionalities are capable of adhering or adsorbing to hydrophobic surfaces. The hydrophobically associating copolymers of the instant invention demonstrate enhanced performance with replacement ratios on the order of 0.35-0.50 over current commercially available poly(DADMAC) treatments.